We examine the potential for a “natural” three-neutrino mixing scheme to satisfy available data and astrophysical arguments. By “natural” we mean no sterile neutrinos, and a neutrino mass hierarchy similar to that of the charged leptons. We seek to satisfy (or solve) (1) accelerator and reactor neutrino oscillation constraints, including LSND, (2) the atmospheric muon neutrino deficit problem, (3) the solar neutrino problem, (4) r-process nucleosynthesis in neutrino-heated supernova ejecta, and (5) cold+hot dark matter models. We argue that putative supernova r-process nucleosynthesis bounds on two-neutrino flavor mixing can be applied directly to three-neutrino mixing in the case where one vacuum neutrino mass eigenvalue difference is dominated by the others. We show that in this “one mass scale dominance” limit, a natural three-neutrino oscillation solution meeting all the above constraints exists only if the atmospheric neutrino data and the LSND data can be explained with one neutrino mass difference. In this model, an explanation for the solar neutrino data can be effected by employing the other independent neutrino mass difference. Such a solution is only marginally allowed by the current data, and proposed long-baseline neutrino oscillation experiments can definitively rule it out. If it were ruled out, the simultaneous solution of the above constraints by neutrino oscillations would then require sterile neutrinos and/or a neutrino mass hierarchy of a different nature than that of the charged leptons. © 1996 The American Physical Society.

Studies of limits on active-sterile neutrino mixing derived from big bang nucleosynthesis (BBN) considerations are extended to consider the dependence of these constraints on the primordial deuterium abundance. This study is motivated by recent measurements of D/H in quasar absorption systems, which at present yield discordant results. Limits on active-sterile mixing are somewhat relaxed for high D/H (≈2×[Formula presented]). For low D/H (≈2×[Formula presented]), no active-sterile neutrino mixing is allowed by currently popular upper limits on the primordial [Formula presented] abundance [Formula presented]. For such low primordial D/H values, the observational inference of active-sterile neutrino mixing by upcoming solar neutrino experiments would imply that [Formula presented] has been systematically underestimated, unless there is new physics not included in standard BBN. © 1996 The American Physical Society.

We discuss neutrino oscillations in curved spacetime. Our heuristic approach can accommodate matter effects and gravitational contributions to neutrino spin precession in the presence of a magnetic field. By way of illustration, we perform explicit calculations in the Schwarzschild geometry. In this case, gravitational effects on neutrino oscillations are intimately related to the redshift. We discuss how spacetime curvature could affect the resonance position and adiabaticity of matter-enhanced neutrino flavor conversion. © 1997 The American Physical Society.

The reported signal at the LSND experiment, when interpreted as neutrino mixing with δm = 6 eV , provides evidence for neutrinos with a cosmologically significant mass. However, attempts to reconcile this interpretation of the experiment with other hints about neutrino properties require a (sterile) fourth neutrino and/or an "inverted" neutrino mass hierarchy. An interpretation of the LSND experiment employing δm = 0.3 eV , with three-generation mixing and a "normal" neutrino mass hierarchy, can just barely be reconciled with the negative results of other laboratory neutrino oscillation experiments and the positive hints of neutrino oscillation from the solar and atmospheric neutrino problems. Though subject to test by by future experiments, such a solution allows (but does not demand) neutrino masses relevant for dark matter. 2 2 2 2

We discuss general relativistic effects in the steady state neutrino-driven "wind" that may arise from nascent neutron stars. In particular, we generalize previous analytic estimates of the entropy per baryon S, the mass outflow rate M, and the dynamical expansion timescale τ . We show that S increases and τ decreases with increasing values of the mass-to-radius ratio describing the supernova core. Both of these trends indicate that a more compact core will lead to a higher number of neutrons per seed nucleus. Such an enhancement in the neutron/seed ratio may be required for successful r-process nucleosynthesis in neutrino-heated supernova ejecta. © 1997. The American Astronomical Society. All rights reserved. dyn dyn

Recent determinations of the deuterium abundance, H/H, in high redshift Lyman limit hydrogen clouds challenge the usual picture of primordial nucleosynthesis based on "concordance" of the calculated light element ( H, He, He, Li) nucleosynthesis yields with the observationally-inferred abundances of these species. Concordance implies that all light element yields can be made to agree with the observationally-inferred abundances (within errors) for single global specifications of the baryon-to-photon ratio, η; lepton number; neutron lifetime; and expansion rate (or equivalently, effective number of light neutrino degrees of freedom N ). Though one group studying Lyman limit systems obtains a high value of H/H (∼ 2 × 10 ), another group finds consistently low values (∼ 2 × 10 ). In the former case, concordance for N = 3 is readily attained for the current observationally-inferred abundances of He and Li. But if the latter case represents the primordial deuterium abundance, then concordance for any N is impossible unless the primordial value of Li/H is considerably larger than the abundance of lithium as measured in old, hot Pop II halo stars. Furthermore, concordance with N = 3 is possible for low H/H only if either (1) the primordial He abundance has been significantly underestimated, or (2) new neutrino sector physics is invoked. We argue that systematic underestimation of both the Li and He primordial abundances is the likely resolution of this problem, a conclusion which is strengthened by new results on He. 2 2 3 4 7 2 -4 -5 4 7 7 2 4 7 4 4 v v v v

Three-neutrino mixing schemes suggested by Cardall & Fuller and Acker & Pakvasa are compared and contrasted. Both of these schemes seek to solve the solar and atmospheric neutrino problems and to account for the possible neutrino oscillation signal in the LSND experiment. These neutrino oscillation schemes have different atmospheric and solar neutrino signatures that will be discriminated by Super-Kamiokande and SNO. They will also have different signatures in proposed long-baseline accelerator and reactor experiments. In particular, both of these schemes would give dramatic (and dramatically different) signals in an "intermediate baseline" experiment, such as the proposed ICARUS detector in the Jura mountains 17 km from CERN. © 1997 Elsevier Science B.V.

We study steady state winds from compact objects in the regime where the wind velocity at infinity is ultrarelativistic. This may have relevance to some models of gamma-ray bursts (GRBs). Particular attention is paid to the case in which neutrinos provide the heating. Unless the neutrino luminosity is very large, L > 10 ergs s , the only allowed steady state solutions are those where energy deposition is dominated by neutrino-antineutrino annihilation at the sonic point. In this case, the matter temperature near the neutron star surface is low, less than 1 MeV for typical neutrino luminosities. This is in contrast to the case for subrelativistic winds discussed in the context of supernovae, where the matter temperature near the neutron star approximates the temperature characterizing the neutrinos. We also investigate the setting of the neutron-to-proton ratio (N/P) in these winds and find that only for large (> 10 MeV) electron-neutrino or electron-antineutrino temperatures is N/P entirely determined by neutrino capture. Otherwise, N/P retains an imprint of conditions in the neutron star. 54 -1